Fermented Agri-Food By-Products from Tubers and Legumes as Next-Generation Functional Ingredients: From Waste Valorisation to Precision Nutrition

Abstract

Processing tubers such as potato, sweet potato, cassava, and yam, as well as legumes such as soybean, pea, chickpea, bean, and lentil, generates substantial quantities of peels, pulps, husks, and press cakes that retain considerable nutritional and functional value despite often being discarded. Microbial fermentation has emerged as a low-cost and scalable approach for valorising these residues into functional ingredients with improved digestibility and enhanced bioactive-compound content. This study synthesises the composition of major tuber and legume by-products, the solid-state and submerged fermentation systems employed for their bioconversion, and the biochemical and functional transformations achieved through fermentation, including improvements in antioxidant activity, prebiotic potential, antihyperglycaemic properties, and protein quality. The emerging applications of these fermented by-products in bakery products, dairy alternatives, snacks, nutraceuticals, and the conceptually related field of gut-microbiome-guided precision nutrition are also examined. Persistent challenges, including compositional variability, safety monitoring, and regulatory classification, are critically evaluated alongside strategies for addressing these limitations. Overall, fermentation-based valorisation of tuber and legume residues represents a scientifically credible and environmentally sustainable strategy for transforming agri-food waste streams into value-added, functional nutrition ingredients.